1. Field of the Invention
The present invention relates to an image forming apparatus of a type wherein a belt-like recording paper carrying member is allowed to electrostatically absorb a sheet of recording paper such as paper and hold it thereon and toner images are successively superimposed on and transferred to the recording paper while the recording paper is being fed along an image transfer unit comprising a plurality of photoconductive or photosensitive drums, and particularly, to a device wherein when a paper jam is developed in the recording paper carrying member and at a back-and-front position of the recording paper carrying member, a means for forcedly ejecting the recording paper located in the neighborhood of the recording paper carrying member is provided to thereby make it possible to facilitate the operation for ejecting the recording paper.
2. Description of the Related Art
As an image forming apparatus such as an electrophotographic copier capable of making a color copy or a laser beam printer, an apparatus of a type which has been disclosed in Japanese Patent Laid-Open No. Sho 59(1984)-155870, for example, is known. In the conventional color electrophotographic copier, a plurality of image carriers such as photosensitive drums for forming color toner images based on information obtained by separating images on the original for every color are provided. Further, an image transfer unit comprising the photosensitive drums is disposed along a recording paper carrying member. This type of copier forms an apparatus of a type wherein while a sheet of paper used as recording paper is being fed in a state in which the paper is being electrostatically carried by a belt-like recording paper carrying member, color toner images from photosensitive drums are successively superposed on and transferred to the paper carried by the recording paper carrying member, is constructed. In the aforementioned apparatus, since the toner images are successively superimposed on and transferred to the paper, the weight of toner carried by the recording paper becomes large, thereby making it possible to have the recording paper and the recording paper carrying member carry the performance for holding large transfer charges in correspondence with the weight of toner.
The apparatus for causing the recording paper carrying member to electrostatically absorb and hold the recording paper as described above needs a means for separating the recording paper from the recording paper carrying member after the color toner images have been transferred to the paper and feeding it to the fixing device. Therefore, a normal image forming apparatus using a recording paper carrying member is used in which a small-diameter roller member is provided at the position where a sheet of recording paper is separated and the function of reducing an electrostatic absorbing force using a means for separating the recording paper owing to an abrupt bend of the recording paper carrying member and a discharger or the like is applied thereto. Further, a method of disposing a separation claw member in a recording paper separation unit incidentally to the above-described separating means, causing the leading end portion of the separation claw member to approach the surface of a recording paper carrying member and separating the recording paper using a guide means based on the separation claw member is used, for example.
In the image forming apparatus, a charging corotron for electrostatically absorbing or sucking and holding the recording paper by the recording paper carrying member, a transfer corotron for transferring a toner image from an image carrier, a separation corotron provided at the position where the recording paper is separated from the recording paper carrying member, a belt destaticizing corotron for removing the charging of the recording paper carrying member after the recording paper has been separated from the recording paper carrying member, etc., are provided along a paper conveying path formed by the recording paper carrying member. By providing the aforementioned corotrons, the image forming apparatus can charge and destaticize the recording paper carrying member and the recording paper. Further, the image forming apparatus performs a function or action for holding the recording paper on the recording paper carrying member, a function or action for separating the recording paper from the recording paper carrying member and a function for transferring the toner image from the image carrier to the recording paper.
In the aforementioned image forming apparatus, there is a case in which a plurality of image forming units are not used depending on the type of color toner image transferred to the recording paper. There are cases where copies are made using, for example, a black monochrome mode and red, blue and yellow monochrome modes or the two of the four colors and the three of the four colors. When the copy mode is set, the image forming apparatus takes the following measures against a toner-image forming image carrier and a toner-image unforming image carrier in order to prevent an omission of the image.
An image forming apparatus described in Japanese Patent Laid-Open No. Hei 1(1989)-96670 is disclosing a means for applying bias to all-color development rollers regardless of the color mode when a two-component developer is employed in a developer unit to thereby prevent carriers of the two-component developer and needless toner from adhering to the image carrier. On the other hand, in a state in which the polarity of the toner electrostatically carried or supported by the recording paper and a charge characteristic of the image carrier are different from each other, when the recording paper passes through the position of the toner-image unforming image carrier, a problem arises that the toner carried by the recording paper is transferred to the image carrier to thereby cause reverse transfer, whereby the image is deteriorated. In order to solve the aforementioned problem, a means for activating a charging means of a toner-image unforming image carrier and an image transfer means to thereby prevent the reverse transfer from being brought to the image carrier has been proposed in an image forming apparatus disclosed in Japanese Patent Laid-Open No. Sho 63(1988)-8665.
However, the image forming apparatus of a type wherein the plurality of image carriers are provided so as to successively superimpose the color toner images on and transfer them to the recording paper (hereinafter called "paper"), is disclosing the means for preventing imperfections in the image transferred to the paper in the course of transfer of the normal color toner image to the paper, but does not take into consideration countermeasures to be taken when a paper jam (jammed paper) or the like takes place. In the conventional image forming apparatus, an operation for processing jammed paper after the jammed paper has been detected, e.g., a method of forcedly ejecting the paper has not been taken into consideration.
Thus, as means for solving the above problems, an apparatus disclosed in Japanese Patent Laid-Open No. Hei 2(1990)-257158, for example, may be constructed as one method. The above-described conventional example shows a paper feeder constructed in such a manner that when a paper jam is developed within a reverse conveying path provided on the downstream side of a fixing device, a sheet of paper extending on a recording paper carrying member can be automatically ejected from an ejection path divided from the position on this side of the paper. However, the aforementioned image forming apparatus has a problem that it is necessary to provide a special tray or the like to accommodate paper ejected in the course of its delivery therein, thereby making the image forming apparatus complex in structure.
The normal image forming apparatus is provided with a function for indicating, based on a self-diagnosis function added to the body thereof, to which position on the paper conveying path the paper remains after the jammed paper has been detected. Further, a means is provided for setting a forced ejection mode for automatically ejecting the paper left in the paper conveying path after the paper has been removed by an operator. Particularly, in a color image forming apparatus of a type wherein four image carriers are arranged along a paper conveying path formed by a recording paper carrying member so as to obtain full-color images of four colors, the number of papers simultaneously carried by the recording paper carrying member inevitably increases. Therefore, the setting of a mode for automatically performing an operation for forcedly ejecting paper simultaneously fed within the paper conveying path is indispensable.
When it is desired to set the mode for forcedly ejecting the paper carried by the recording paper carrying member as described above, a control information mode for deactivating a charging corotron for causing the recording paper carrying member to electrostatically absorb a sheet of paper ejected as a miss copy in blank paper and a separation corotron for peeling or separating the paper from the recording paper carrying member is often used. However, when the control information mode is set, each image carrier is charged by a charging means. When a transfer corotron is in a deactivated state, there is a case where the feeding of the paper to the recording paper carrying member alone cannot make a conveying operation in a state in which the paper is being held by the recording paper carrying member. When the paper is separated from the recording paper carrying member and is attracted by the image carrier, the paper plunges into a cleaning device, thereby causing inconvenience that a new paper jam is developed. The aforementioned phenomenon tends to greatly occur in the image carrier located upstream of a traveling path of the recording paper carrying member in particular.
On the other hand, when the transfer corotron provided so as to correspond to the image carrier is activated, the frequency of occurrence of inconvenience that the paper is wound around the image carrier if the charging corotron for attracting the paper to the recording paper carrying member is in a deactivated state, is less reduced but is completely unavoidable. When the separation corotron for separating the paper from the recording paper carrying member is deactivated regardless of the actuation of the transfer corotron associated with the image carrier, a problem arises that the mistake of separation of the paper from the recording paper carrying member is made, so that the paper plunges into other device located on the downstream side of the separation unit.